This invention relates in general to the packaging of integrated circuits and in particular to the method of encapsulating a hermetically sealed integrated circuit in plastic, utilizing the latest of conductor lead bonding, plastic and film technology, and to a new and improved plastic encapsulated hermetically sealed integrated circuit package incorporating this technology.
The packaging of integrated circuits, commonly referred to as chips or dice, has been the subject of much study. The art teaches several ways of packaging chips, but perhaps the most predominant process includes as part of the process the bonding of lead wires from the chip to a metal leadframe. This process is expensive, time-consuming, error-prone and requires the utmost care in handling to prevent breakage due to the fragility of the wires, thereby increasing the cost per package considerably.
To date, therefore, there is a need for a reliable, low-cost packaging process, utilizing automatic techniques, taking advantage of present day hermetically sealed chips and taking advantage of gang-bonding techniques and plastic technology, to form a hermetically sealed plastic encapsulated integrated circuit package.
One of the advantages of such a packaging process is the reduction in the cost of packaging such chips by:
1. utilizing industry standard 35 mm film with sprocket holes which are precisely located and thus can be used as locating holes to index the various elements that make up the package during the process; PA1 2. utilizing such a film, the patterns of connector leads formed thereon are supported during handling thus eliminating the danger of damage due to fragile connections, etc; PA1 3. utilizing such a film, the hermetically sealed bump die is indexed into place relatitve to the film while the film is still co-planar and while so indexed, is gang-bonded thereto; PA1 4. utilizing such a film with the bonded die being supported by the film, the film serves as a carrier for safer handling of both the connector leads and die; PA1 5. utilizing such a film as a carrier and while so supported on said film, the die and the gang-bonded connections of the connector leads thereto are tested, thus eliminating the cost of the remaining steps in the process otherwise involved, if testing the entire package were to await the final step in the process; PA1 6. providing a metal heat sink having means for supporting the die and the ground straps so that the carrier and leads remain co-planar throughout, thus eliminating the costly prior art step of bending the leads, as for example, bending the ground straps to the plane of the heat sink; and PA1 7. utilizing a single transfer mold which positions the die and the film together with the heat sink so that the die can be accurately indexed and thermally and mechanically connected to the heat sink, so that the ground straps are pulse-soldered to the heat sink in one step, with the sprocket holes again used as locater holes, and, thereafter, without removal from the same mold, selectively encapsulating the assembly in plastic.
It should also be apparent from the foregoing that there are a number of aspects of this invention which represent advantages over the prior art, in addition to the reduction of costs as represented by the steps set forth above, which are:
there is a one-step bonding of the die to the connector leads and thus this lead interface step becomes essentially the electronic package with direct electrical communication established with the chip,
the film carrier and its attached die are in one step, electrically attached to the heat sink and, in one step, made integral with the heat sink by the plastic encapsulation.
Most importantly is the reduction in the number of electrical interfaces, i.e., the one step gang-bonding of the die of the film carrier (as distinguished from individually bonding wire leads from the die to a metal leadframe) and the one step connection of the film carrier and die to the heat sink. It is well known that any reduction in interface connection steps improves the reliability of the circuit since each interface required affects the mean time before failure (MTBF) of a device. With this invention the reliability of these packages is improved considerably.
From the foregoing, it should also be apparent that also involved in this invention is a new and improved plastic encapsulated hermetically sealed integrated circuit or die, of the leadless package type, having a selectively configured heat sink with means of elevating the die above the main surface or plane of the heat sink and with means for elevating the connection of the ground straps so that all the lead conductors still disposed on a film in said package are co-planar, and forming a reliable circuit ready for utilization in an electronic device.